Process for spinning fibers of poly(4-methyl-1-pentene)



United States Patent 3,415,921 PROCESS FOR SPINNING FIBERS 0F POLY(4-METHYL-1-PENTENE) Gerald A. McFarren, Wilmington, Del., assignor to Hercules Incorporated, a corporation of Delaware No Drawing. Filed Mar. 1, 1965, Ser. No. 436,270 1 Claim. (Cl. 264-176) ABSTRACT OF THE DISCLOSURE A process for spinning fibers of high molecular weight poly(4-methyl-l-pentene) comprising charging a polymer crumb wet with diluent to an extruder, adding diluent downstream of the feed point and extruding the resultant solution at high temperature.

This invention relates to a process of preparing an oriented high molecular weight poly(4-methyl-1-pentene) fiber, which fiber exhibits high temperature strength retention and good abrasion resistance.

It is well known that 4-methyl-l-pentene can 'be polymerized to a high molecular weight crystalline polymer having a melting point above about 230 C. However, when the high molecular weight polymers are spun, as in a melt spinning process, degradation of the polymer is so severe because of the high temperature required to avoid melt fracture, that the resultant fiber has a greatly reduced molecular weight, and the fiber is weak, with poor high temperature strength and very poor abrasion resistance. In fact, as pointed out in US. 2,842,532, in order to spin a fiber capable of orientation, it is necessary to reduce the molecular weight of the polymer to a point such that the inherent viscosity is within the range of 0.8 to 1.6. The necessity of using a low molecular weight polymer is even further emphasized by US. 2,957,225, where it is set forth that the molecular weight of the polymer must be such that it has a melt index within the range of 0.1 and 44 for the polymer to be within the limits of the spinning process. Thus, the prior art teaches that only a relatively low molecular weight poly(4-methyl-1- pentene) can be melt spun into an orientable fiber and, even then, there is severe degradation of the polymer. As a result, the fibers previously produced from poly(4- methyl-l-pentene) have exhibited only low strength retention at elevated temperatures and poor abrasion resistance.

Solution spinning of a high molecular weight poly(4- methyl-l-pentene) has likewise met with frustration because such processes require long periods of holding the solution at high temperature for degassing, with the result that the fiber spun therefrom has a greatly reduced molecular weight. Hence, attempts to solution spin a high molecular weight polymer results in the production of only a low molecular weight fiber since the solutions of such polymers cannot be degassed at a temperature below about 190 C. due to their high viscosity, and rapid degradation of the polymer takes place. Accordingly, it has previously been possible to spin only low molecular weight polymers by solution spinning processes.

Now, in accordance with this invention, fibers of poly- (4-methyl-l-pentene), having a reduced specific viscosity greater than about 5, can be produced by feeding into a heated extruder solid poly(4-methyl-l-pentene) having a reduced specific viscosity of at least 5, and introducing at a point along the extruder and removed from the feed point sufiicient inert liquid diluent to form within the extruder at an extrusion temperature of about 160 to 285 C. a solution containing about 20 to about 60% by weight of said poly(4-methyl-1-pentene) while heating "ice to said extrusion temperature, extruding a filament from the solution formed, removing the diluent from the extruded filament and then stretching the filament to produce an oriented fiber.

In order to produce high molecular weight fibers of poly(4-methyl-1-pentene), it is necessary to carry out the spinning of a high molecular weight polymer in such a fashion that excessive degradation of the polymer does not occur during the spinning operation. This can be accomplished only by avoiding the high temperatures required for melt spinning and the long hold-up times at elevated temperatures required in normal solution spinning operations. This can be achieved in accordance with the process of this invention by forming in a screw extruder fitted with a suitable spinhead a solution of the polymer and diluent, spinning the solution into filaments, and passing the extruded filaments through a solvent re moval means to remove the solvent from the fiber. One means of carrying out such a process is to charge dry polymer flake to a vented screw extruder, and introduce the diluent to the extruder through its vent. The amount of diluent introduced must be sufiicient to form within the area of the spinhead of the extruder a 20% to 60% by weight solution of the polymer in the diluent at a temperature of about C. to about 285 C. If the amount of polymer in the diluent is less than about 20%, then the viscosity of the solution will be low, thereby causing difliculties during spinning and loss of economic advantages due to the increased amount of diluent which must be removed after spinning. On the other hand, if the amount of polymer in the diluent is greater than about 60%, undesirably higher temperatures will be required to obtain and maintain a spinnable solution, thereby causing degradation of the polymer. Another means of carrying out the process is to charge to the extruder as feed wet polymer crumb, such as that obtained by mechanical extraction of diluent from the polymer as it comes from the polymerization process, and introducing the additional diluent required to form the desired solution at the vent of the extruder. The diluent wet crumb of polymer will contain varying amounts of diluent, depending upon the method and length of time of extraction. For purposes of the present invention, the polymer crumb will contain from a very small amount up to but not exceeding about 30% diluent since amounts above 30% in general cause difiiculties at the feed point due to the tendency of diluent to squeeze out and drip from the back of the extruder thus causing variable polymer concentrations as well as mechanical problems. The polymer, whether in the form of dry polymer flake or diluent wet crumb, is mixed with the diluent as it is forced through the extruder and is dissolved in the diluent on being heated in the extruder to the spinning temperature. As already pointed out above, the spinning operation is carried out at a temperature of from about 160 C. to about 285 C.

By forming in the screw extruder, a solution of the polymer in a diluent, in accordance with this invention, the long holding period at elevated temperature which is required for degassing in ordinary solution spinning is avoided. At the same time, it provides a means of obtaining and spinning a relatively dilute solution of the polymer which can be spun at lower temperatures and hence greatly minimizes polymer degradation.

Any inert liquid organic diluent can be used as the diluent for the preparation of the solution used in the abovedescribed spinning operation. Particularly suitable are hydrocarbon and chlorinated hydrocarbon diluents. Such hydrocarbons can be aliphatic, alicyclic or aromatic, saturated or unsaturated. Exemplarly of suitable diluents that can be used are decane, decene, dodecane, cetane, cy-mene, menthane, bicyclohexyl, hxahydronaphthalene, decahydronaphthalene, dichlorobenzene, mineral oil,

paraffin oil, etc. Generally there will be used as diluent the commercially available mixtures of such hydrocarbons or chlorinated hydrocarbons. While the polymer is not appreciably soluble in such diluents at room temperature, solvation occurs when the mixture is heated in the extruder. Preferably the diluent will have a boiling point within the range of from about 175 C. to about 300 C.

As pointed out above, after extrusion of the filament, the solvent is removed. This can be done by any of the standard procedures used in dry spinning. For example, it can be passed through a typical solvent spinning-type chimney or by any other means of contacting the filament with a stream (generally counter current) of heated gas, as for example, air, nitrogen, carbon dioxide, or steam, to remove the solvent.

Following the solvent removal from the filament, it can be wound on a bobbin and then later subjected to the standard stretching procedures for orienting a fiber or the orientation can, of course, be carried out immediately. The stretching or orientation is carried out at elevated temperature, generally at a temperature within the range of from about 100 C. to about 200 C. The degree of stretching will, as is well recognized by those skilled in the art, depend upon such interrelated factors as RSV of the fiber, concentration of the solution as spun, the spinning temperature, the size of the spinning orifice, the rate of spinning, the rate of solvent removal, the amount of draw down, the final denier of the fiber desired, and the physical properties desired in the final fiber, i.e. tenacity, modulus and elongation. In general, the filament will be drawn from about 250% to about 1300%. Ohviously, many other fiber treatments can be applied, if desired, following the extrusion of the fiber, as for example, sizing of the fiber, dyeing, etc., and these steps of orientation, etc., can be carried out in any desired order after the extrusion of the filament and removal of the solvent therefrom.

By utilizing the above-described spinning procedure, no degassing operation is required and the spinning solution is held at the elevated temperature for only the brief period needed in the extruder to raise it to the spinning temperature, with the result that polymer degradation is greatly minimized. Thus, it is possible to produce high molecular weight low denier fibers without appreciable polymer degradation or melt fracture, which fibers, on orientation, have execptional physical properties not exhibited by the low molecular weight poly(4-methyl-1- pentene). Specifically, at 100 C. they retain at least about 50% of their ambient strength properties. In addition, the fibers produced by the process of this invention are round rather than flattened, and, consequently, have a vastly improved abrasion resistance over that of the prior art low molecular weight fibers. Because of their high temperature strength retention, they can, for example, be used as reinforcing fibers in tires, for use in fabric for dust bags used in high temperature applications, and in other uses where the fiber is exposed to high temperatures. The manyfold improvement in abrasion resistance enables the use of these fibers for blending with cotton to improve the abrasion resistance of the cotton.

The high molecular weight poly(4-methyl-l-pentene) fibers produced in accordance with this invention are prepared by spinning a poly(4-methyl-1-pentene) having a molecular weight such that the RSV of the fiber is greater than about 5. Such polymers can be prepared by any of the well known processes for polymerizing 4- methyl-1-pentene. Generally, the polymerization process is carried out by contacting 4-methyl-1-pentene with a transition metal compound-alkyla1uminum catalyst in an inert organic liquid diluent under relatively mild conditions of temperature and pressure. After treatment to remove or inactivate the catalyst residues, the polymer, which is insoluble in the diluent at room temperature, is separated by filtration, centrifugation, or other convenient means, and the polymer crumb so obtained can be used directly for preparation of the spinning solution, as described above, or the polymer can be dried and fed to the extruder as such.

The following examples will illustrate the preparation of the high molecular weight poly(4-methyl-1-pentene) fibers in accordance with this invention. All parts and percentages are by weight unless otherwise stated. The molecular weight of the polymers and fibers is shown by the reduced specific viscosity (RSV) given for each. By the term Reduced Specific Viscosity is meant the /c determined on a 0.1% solution of the polymer in decahydronaphthalene at 135 C.

A typical polymerization of 4-methyl-l-pentene was carried out as follows:

A polymerization vessel with a nitrogen atmosphere was charged with 170 pounds of a dry commercial mixture of chiefly aliphatic hydrocarbons having a boiling point range of 210230 C., and after heating to 55 C., 1.3 pounds of a 25 solution of diethylaluminum chloride in the same diluent was added, the mixture was agitated for 30 minutes at 55 C. and then 600 millimoles of a titanium catalyst was added. The titanium catalyst was prepared by adding at 0 C. one mole of titanium tetrachloride to an amount of a 25% solution of ethylaluminum sesquichloride, in the above hydrocarbon diluent, equal to 0.6 mole of diethylaluminum chloride and 0.6 mole of ethylalurninum dichloride. This mixture was held at 0 C. for 16 hours, then heated at 100 C. for 4 hours and filtered. The precipitate was washed three times with the hydrocarbon diluent and then diluted to 0.5 molar in titanium with the hydrocarbon and used in the polymerization reaction. With the temperature in the polymerization held at 55 C., 22 pounds of 4-methyl-l-pentene was added and at intervals of 5 to 10 minutes, additional 4-methyl-1-pentene was added in increments of 5 pounds until a total of pounds had been added. The polymerization was continued at C. for a total of 6 hours, after which it was shortstopped by adding 2 liters of butanol. The polymer slurry was heated to 80 C. and a mixture of 20 gallons of water, 4 pounds of sodium hydroxide and 1.6 pounds of 50% gluconic acid was added and the whole was agitated for 1 hour at 80 C. The aqueous phase was separated, the polymer slurry agitated at 80 C. for 1 hour with 20 gallons of water and again the aqueous phase was separated. The polymer slurry was then heated to 75 C. under low vacuum to distill off the remaining water, filtered and reslurried with 20 gallons of heptane at C. for 30 minutes and again filtered. The filter cake was pressed as free of heptane as possible and part was retained as such, as polymer crumb, and part was stabilized and dried at 40 C. under vacuum for 16 hours. Tfhe poly(4-methyl-1-pentene) so produced had an RSV o 7.7.

Example 1 The polymer crumb of poly(4-methyl-1-pentene) used in this example was prepared as described above, had an RSV of 7.7 and contained about of polymer by weight. The wet crumb was fed into a standard l-inch vented extruder set at 220 C. and sufficient diluent comprising a mixture of aliphatic hydrocarbons boiling within the range of 175 to 200 C. was metered under p ressure into the extruder vent to give a spinning solution containing about 25% by weight of polymer. This solution was extruded into yarn at 210 C. through a 35-hole spinneret at the rate of 300 meters/minute. The yarn was passed downward through a stream of nitrogen at 200 C. to remove the solvent and was collected on a bobbin. The 850/35 yarn so obtained was drawn at a draw ratio of 6.521 through an oven heated to 220 C. and was taken up on a bobbin at 126 feet/minute. The physical properties of the yarn so obtained were measured at 25 C. The tenacity in grams per denier was 4.1 (measured on an Instrom at an extension rate of per minute at 25 C.) and the elongation was 26%. The RSV of the yarn was 6.5.

Example 2 The dried poly(4-methyl-1-pentene), having an RSV of 7.7 and prepared as described above, was used in this example. The dry polymer was fed to the extruder and the diluent was metered in as described in Example 1 to form a 22% by weight solution of the polymer in a mixture of aliphatic hydrocarbons having a boiling range of 210 to 235 C., which solution was spun at 200 C. into 925/35 yarn at 300 meters/minute. The yarn was passed through a counter-current stream of superheated steam (at about 150 C.) in a drying chimney, and taken up on a yarn bobbin. It was then drawn in a 210 C. air oven at a draw ratio of 7:1. The yarn so obtained had an RSV of 6.5, a tenacity of 4.8 grams per denier and a breaking elongation of 24%.

What I claim and desire to protect by Letters Patent is:

1. The process of preparing oriented fibers of poly(4- methyl-l-pentene) which comprises the steps of (1) feeding into a heated extruded solid poly(4-rnethyll-pentene) having a reduced specific viscosity greater than about 5 as measured on a 0.1% solution in decahydronaphthalene at 135 C. in the form of diluent wet polymer crumb containing less than about 30% diluent.

(2) introducing at a point along the extruder and removed from the feed point suflicient inert liquid diluent to form within the extrutler at an extrusion temperature of about 160 C. to about 285 C. a solution containing about 20% to about by weight of said poly(4-n1ethyl-l-pentene), while heating to said extrusion temperature,

(3) extruding the resulting solution in the form of a filament,

(4) evaporating the diluent from the filament, and

(5) orienting the filament by stretching said filament.

References Cited UNITED STATES PATENTS 2,214,442 9/1940 Spanagel 264--211 3,017,238 1/1962 Levine et a1. 264-476 2,842,532 7/1958 Campbell 264-176 FOREIGN PATENTS 646,186 8/1962 Canada. 849,033 9/ 1960 Great Britain.

JULIUS FROME, Primary Examiner. H. MINTZ, Assistant Examiner.

US. Cl. X.R. 264-205, 210 

